This article deals with so-called ''core'' utilities on a GNU/Linux system, such as ''less'', ''ls'', and ''grep''. The scope of this article includes - ''but is not limited to'' - those utilities included with the GNU {{Pkg|coreutils}} package. What follows are various tips and tricks and other helpful information related to these utilities. If sections grow too detailed, please split into separate articles.

+

This article deals with so-called ''core'' utilities on a GNU/Linux system, such as ''less'', ''ls'', and ''grep''. The scope of this article includes, but is not limited to, those utilities included with the GNU {{Pkg|coreutils}} package. What follows are various tips and tricks and other helpful information related to these utilities.

== cat ==

== cat ==

Line 18:

Line 18:

[[Wikipedia:cat_(Unix)|cat]] (''catenate'') is a standard Unix utility that concatenates and lists files.

[[Wikipedia:cat_(Unix)|cat]] (''catenate'') is a standard Unix utility that concatenates and lists files.

−

* As ''cat'' is not a shell built-in, in many occasions you may find more convenient to use a redirection, for example in scripts, or if you care a lot about performance. In fact {{ic|$ < ''file''}} does the same of {{ic|$ cat ''file''}}.

+

* As ''cat'' is not a shell built-in, in many occasions you may find more convenient to use a [[wikipedia:Redirection (computing)|redirection]], for example in scripts, or if you care a lot about performance. In fact {{ic|< ''file''}} does the same of {{ic|cat ''file''}}.

* To append multiple lines to a file a construct like this one is used:

* To append multiple lines to a file a construct like this one is used:

Line 52:

Line 52:

The environment variable {{ic|GREP_COLORS}} may be used to specify different colors than the defaults.

The environment variable {{ic|GREP_COLORS}} may be used to specify different colors than the defaults.

−

== ifconfig ==

+

== ip ==

+

[[wikipedia:Iproute2|ip]] allows you to show information about network devices, IP addresses, routing tables and other objects in the Linux [[Wikipedia:Internet Protocol|IP]] software stack. By appending various commands, you can also manipulate or configure most of these objects.

−

[[Wikipedia:ifconfig|ifconfig]] (''interface configuration'') is a system administration utility in Unix-like operating systems to configure, control, and query TCP/IP network interface parameters from a command line interface (CLI) or in system configuration scripts.

+

{| class="wikitable" border="1" cellpadding="5" cellspacing="0"

+

! Object !! Purpose !! manpage

+

|-

+

| ip addr || protocol address management || ip-address

+

|-

+

| ip addrlabel || protocol address label management || ip-addrlabel

+

|-

+

| ip l2tp || tunnel ethernet over IP (L2TPv3) || ip-l2tp

+

|-

+

| ip link || network device configuration || ip-link

+

|-

+

| ip maddr || multicast addresses management || ip-maddress

+

|-

+

| ip monitor || watch for netlink messages || ip-monitor

+

|-

+

| ip mroute || multicast routing cache management || ip-mroute

+

|-

+

| ip mrule || rule in multicast routing policy db

+

|-

+

| ip neigh || neighbour/arp tables management|| ip-neighbour

+

|-

+

| ip netns || process network namespace management || ip-netns

+

|-

+

| ip ntable || neighbour table configuration || ip-ntable

+

|-

+

| ip route || routing table management || ip-route

+

|-

+

| ip rule || routing policy database management || ip-rule

+

|-

+

| ip tcp_metrics || management for TCP Metrics || ip-tcp_metrics

+

|-

+

| ip tunnel || tunnel configuration || ip-tunnel

+

|-

+

| ip tuntap || manage TUN/TAP devices

+

|-

+

| ip xfrm || manage IPSec policies || ip-xfrm

+

|}

−

It is deprecated: the alternative is called [[Configuring_Network|ip]].

+

The help command is available for all objects. For example, typing {{ic|ip addr help}} will show you the command syntax available for the address object.

+

+

The [[Network Configuration]] article shows how the ''ip'' command is used in practice for various common tasks.

== less ==

== less ==

Line 107:

Line 146:

[[Vim]] (''visual editor improved'') has a script to view the content of text files, compressed files, binaries, directories. Add the following line to your shell configuration file to use it as a pager:

[[Vim]] (''visual editor improved'') has a script to view the content of text files, compressed files, binaries, directories. Add the following line to your shell configuration file to use it as a pager:

{{hc|~/.bashrc|2=alias less='/usr/share/vim/vim73/macros/less.sh'}}

{{hc|~/.bashrc|2=alias less='/usr/share/vim/vim73/macros/less.sh'}}

+

+

There is also an alternative to ''less.sh'' macro, which may work as the {{ic|PAGER}} environment variable. Install {{AUR|vimpager-git}} and add the following to your shell configuration file:

+

{{hc|~/.bashrc|2=

+

export PAGER='vimpager'

+

alias less=$PAGER

+

}}

+

+

Now programs that use the {{ic|PAGER}} environment variable, like [[git]], will use ''vim'' as pager.

== ls ==

== ls ==

Line 126:

Line 173:

alias mkdir='mkdir -p -v'

alias mkdir='mkdir -p -v'

The {{ic|-v}} switch make it verbose.

The {{ic|-v}} switch make it verbose.

−

{{Note|If you want just a temporary directory a better alternative may be [[Wikipedia:Temporary file|mktemp]] (''make termporary''): {{ic|$ mktemp -p}}.

+

{{Tip|If you want just a temporary directory a better alternative may be [[Wikipedia:Temporary file|mktemp]] (''make termporary''): {{ic|mktemp -p}}.

}}

}}

== mv ==

== mv ==

−

[[Wikipedia:mv_(Unix)|mv]] (''move'') is a command to move and rename files and directories. It could be very dangerous so it is prudent to limit its scope:

+

[[Wikipedia:mv_(Unix)|mv]] (''move'') is a command to move and rename files and directories. It can be very dangerous so it is prudent to limit its scope:

alias mv=' timeout 8 mv -iv'

alias mv=' timeout 8 mv -iv'

This alias suspends ''mv'' after eight seconds, asks confirmation to delete three or more files, lists the operations in progress and does not store itself in the shell history file if the shell is configured to ignore space starting commands.

This alias suspends ''mv'' after eight seconds, asks confirmation to delete three or more files, lists the operations in progress and does not store itself in the shell history file if the shell is configured to ignore space starting commands.

Line 137:

Line 184:

== rm ==

== rm ==

−

[[Wikipedia:rm_(Unix)|rm]] (''remove'') is a command to delete files and directories. It could be very dangerous so it is prudent to limit its scope:

+

[[Wikipedia:rm_(Unix)|rm]] (''remove'') is a command to delete files and directories. It can be very dangerous so it is prudent to limit its scope:

alias rm=' timeout 3 rm -Iv --one-file-system'

alias rm=' timeout 3 rm -Iv --one-file-system'

This alias suspends ''rm'' after three seconds, asks confirmation to delete three or more files, lists the operations in progress, does not involve more than one file systems and does not store itself in the shell history file if the shell is configured to ignore space starting commands. Substitute {{ic|-I}} with {{ic|-i}} if you prefer to confirm even for one file.

This alias suspends ''rm'' after three seconds, asks confirmation to delete three or more files, lists the operations in progress, does not involve more than one file systems and does not store itself in the shell history file if the shell is configured to ignore space starting commands. Substitute {{ic|-I}} with {{ic|-i}} if you prefer to confirm even for one file.

Line 147:

Line 194:

Here is a handy [http://sed.sourceforge.net/sed1line.txt list] of ''sed'' one-liners examples.

Here is a handy [http://sed.sourceforge.net/sed1line.txt list] of ''sed'' one-liners examples.

−

{{Note|More powerful alternatives are awk and even Perl language.}}

+

{{Tip|More powerful alternatives are [[Wikipedia:AWK|AWK]] and even [[Wikipedia:Perl|Perl]] language.}}

== seq ==

== seq ==

Line 155:

Line 202:

== shred ==

== shred ==

−

[[Wikipedia:Shred_(Unix)|shred]] is a command to securely delete files and directories. It could be very dangerous so it is prudent to limit its scope:

+

[[Wikipedia:Shred_(Unix)|shred]] is a command to securely delete files and directories. It can be very dangerous so it is prudent to limit its scope:

alias shred=' timeout 3 shred -v'

alias shred=' timeout 3 shred -v'

This alias suspends ''shred'' after three seconds, lists the operations in progress, and does not store itself in the shell history file if the shell is configured to ignore space starting commands.

This alias suspends ''shred'' after three seconds, lists the operations in progress, and does not store itself in the shell history file if the shell is configured to ignore space starting commands.

This article deals with so-called core utilities on a GNU/Linux system, such as less, ls, and grep. The scope of this article includes, but is not limited to, those utilities included with the GNU coreutils package. What follows are various tips and tricks and other helpful information related to these utilities.

Contents

cat

cat (catenate) is a standard Unix utility that concatenates and lists files.

As cat is not a shell built-in, in many occasions you may find more convenient to use a redirection, for example in scripts, or if you care a lot about performance. In fact < file does the same of cat file.

To append multiple lines to a file a construct like this one is used:

$ cat << EOF >> path/filefirst line
...
last line
EOF

If you need to cat file lines in reverse order, there is a utility called tac (cat reversed).

grep

grep (from ed's g/re/p, global/regular expression/print) is a command line text search utility originally written for Unix. The grep command searches files or standard input globally for lines matching a given regular expression, and prints them to the program's standard output.

Colored output

To use the default colors for grep, write the following entry to your shell configuration file, e.g. if using Bash:

~/.bashrc

alias grep='grep --color=auto'

Alternatively, you can set the GREP_OPTIONSenvironment variable bearing in mind this may break some scripts that use grep[1]:

export GREP_OPTIONS='--color=auto'

To include file line numbers in the output, add -n:

alias grep='grep -n --color=auto'

The environment variable GREP_COLORS may be used to specify different colors than the defaults.

ip

ip allows you to show information about network devices, IP addresses, routing tables and other objects in the Linux IP software stack. By appending various commands, you can also manipulate or configure most of these objects.

Object

Purpose

manpage

ip addr

protocol address management

ip-address

ip addrlabel

protocol address label management

ip-addrlabel

ip l2tp

tunnel ethernet over IP (L2TPv3)

ip-l2tp

ip link

network device configuration

ip-link

ip maddr

multicast addresses management

ip-maddress

ip monitor

watch for netlink messages

ip-monitor

ip mroute

multicast routing cache management

ip-mroute

ip mrule

rule in multicast routing policy db

ip neigh

neighbour/arp tables management

ip-neighbour

ip netns

process network namespace management

ip-netns

ip ntable

neighbour table configuration

ip-ntable

ip route

routing table management

ip-route

ip rule

routing policy database management

ip-rule

ip tcp_metrics

management for TCP Metrics

ip-tcp_metrics

ip tunnel

tunnel configuration

ip-tunnel

ip tuntap

manage TUN/TAP devices

ip xfrm

manage IPSec policies

ip-xfrm

The help command is available for all objects. For example, typing ip addr help will show you the command syntax available for the address object.

less

less is a terminal pager program used to view the contents of a text file one screen at a time. Whilst similar to other pages such as
more and pg, less offers a more advanced interface and complete feature-set.

lesspipe also grants less the ability of interfacing with files other than archives, serving as an alternative for the specific command associated for that file-type (such as viewing HTML via html2text).

Re-login after installing lesspipe in order to activate it, or source /etc/profile.d/lesspipe.sh.

Vim as alternative pager

Vim (visual editor improved) has a script to view the content of text files, compressed files, binaries, directories. Add the following line to your shell configuration file to use it as a pager:

~/.bashrc

alias less='/usr/share/vim/vim73/macros/less.sh'

There is also an alternative to less.sh macro, which may work as the PAGER environment variable. Install vimpager-gitAUR and add the following to your shell configuration file:

~/.bashrc

export PAGER='vimpager'
alias less=$PAGER

Now programs that use the PAGER environment variable, like git, will use vim as pager.

ls

ls (list) is a command to list files in Unix and Unix-like operating systems.

Colored output can be enabled with a simple alias. File ~/.bashrc should already have the following entry copied from /etc/skel/.bashrc:

alias ls='ls --color=auto'

The next step will further enhance the colored ls output; for example, broken (orphan) symlinks will start showing in a red hue. Add the following to your shell configuration file:

~/.bashrc

eval $(dircolors -b)

man

man (manual page) is a form of online software documentation usually found on a Unix or Unix-like operating system. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts. See Man Pages.

mkdir

mkdir (make directory) is a command to create directories. To create a directory and its whole hierarchy, -p switch is used, if not a error is printed. As users are supposed to know what they want, -p switch may be used as a default.

alias mkdir='mkdir -p -v'

The -v switch make it verbose.

Tip: If you want just a temporary directory a better alternative may be mktemp (make termporary): mktemp -p.

mv

mv (move) is a command to move and rename files and directories. It can be very dangerous so it is prudent to limit its scope:

alias mv=' timeout 8 mv -iv'

This alias suspends mv after eight seconds, asks confirmation to delete three or more files, lists the operations in progress and does not store itself in the shell history file if the shell is configured to ignore space starting commands.

rm

rm (remove) is a command to delete files and directories. It can be very dangerous so it is prudent to limit its scope:

alias rm=' timeout 3 rm -Iv --one-file-system'

This alias suspends rm after three seconds, asks confirmation to delete three or more files, lists the operations in progress, does not involve more than one file systems and does not store itself in the shell history file if the shell is configured to ignore space starting commands. Substitute -I with -i if you prefer to confirm even for one file.

sed

sed (stream editor) is a Unix utility that parses and transforms text.